What is a stanza of 9 lines called?

A Triplet, as in:

Do not go gentle into that good night.

Old age should burn and rave at close of day,

Rage, Rage against the dying of the light.

The poem is made up of 5 triplets (such as this, the first one in rhyme scheme aba) and a quatrain at the end (four-line stanza, rhyme scheme abab).